Mapping free-carrier diffusion in GaAs with radiative and heat-generating recombination

We use a tightly focused laser along with optical and thermal imaging to measure the diffusion-driven, free-carrier distribution in a GaAs/GaInP heterostructure. We find that temperature profiles are broader than their luminescence counterparts. This observation is consistent with how the underlying recombination mechanisms depend on carrier density: the rate of heat generation should be approximately proportional to the density of carriers, while the radiative rate should scale with the density squared. We show that the square root of the light signal follows the heat profile, giving consistent, independent measurements of the local carrier density.